The present invention relates in general to thrust reversers for jet engines, more particularly to reversers of the so-called cascade type, and even more particularly still, to xe2x80x9cnaturalxe2x80x9d cascade-type reversers.
Cascade-type reversers employ:
to create a discharge opening in the cowling of the engine nacelle: an opening formed in the said cowling, which opening is closed, when in a direct-thrust mode, by a sliding cowl and which is uncovered, in a thrust-reversal mode, by the downstream translation (with reference to the direction of flow of the gases) of the said sliding cowl, a fan duct being defined between an interior skin and an exterior skin into which the interior skin of the sliding cowl is incorporated in a direct-thrust mode, the said opening being equipped with cascades which are shaped so as to direct the reversed jet, and
to substantially block the cold stream (fan air) flowing through the fan duct and deflect it forward through the cascades of the opening thus uncovered in the cowling means the nature of which depends on the ratio between the radius of the said exterior skin of the fan duct and that of the interior skin thereof.
Thus, when this ratio is constant, it is necessary, in order to deflect the cold stream (i.e. the fan flow), to provide a series of small blocker doors which are articulated, on the one hand, to the said sliding cowl and, on the other hand, via a link rod, to the inner fixed structure opposite and which position themselves across the fan duct when the sliding cowl is translated downstream.
When, by contrast, at some point on the fan duct this ratio between the radii has a minimum value, which occurs when the engine forms a bulge whose shape is assumed by the said interior skin, it is possible to take advantage of this geometry to dispense with the small blocker doors and their link rods and block the fan duct using the sliding cowl itself. To do this, a more upstream part of the interior skin of the fan duct is integrated into it by thus giving the upstream interior end of the sliding cowl a spoiler-type configuration which, at the end of travel into the deployed position of the sliding cowl, positions itself circumferentially tangent to the said bulge and thus substantially blocks the fan duct.
The resultant type of reverser is what is known as a xe2x80x9cnaturalxe2x80x9d cascade-type reverser, the sliding cowl xe2x80x9cnaturallyxe2x80x9d blocking the fan duct.
For further details on this type of reverser, reference may be made to FR-A-2 132 380, FR-A-2 349 738 and U.S. Pat. No. 4,232,516.
Although the use of the sliding cowl itself for blocking the fan duct has the advantage of reducing the complexity of the structure by omitting the blocker doors and link rods, it does by contrast present a number of limitations.
Integrating this spoiler-type part into the sliding cowl lengthens the latter on the upstream side which means that the sliding cowl has to be translated over a longer distance to uncover the opening formed in the nacelle cowling. It then follows that use has to be made of actuators which have a longer stroke in order to bring about the desired displacement.
Furthermore, in order to be able to remove and refit the sliding cowl for installation and maintenance purposes by sliding it along rails, it is necessary that the radius of the upstream end of the interior skin of the sliding cowl (that is to say the tip of the spoiler part) be greater than the maximum radius of the interior skin of the fan duct (that is to say the bulge). It then follows that, when the sliding cowl is in a thrust-reversal mode, there still remains some leakage of cold stream in direct thrust between the spoiler part of the sliding cowl and the bulge of the interior skin of the fan duct.
From another viewpoint, the closer the spoiler part of the sliding cowl is to the bulge, the further away will be the upstream face of the sliding cowl from the downstream end of the cascade assembly. This upstream face is made up of a partition which follows on from the spoiler part and which extends outwards from the interior wall of the sliding cowl towards its exterior wall, without reaching the latter, the space left unoccupied forming an access to a cavity in the sliding cowl to house the cascade assembly in the direct-thrust mode.
When, in a thrust-reversal mode, the spoiler part of the sliding cowl is near to the bulge, the partition is appreciably downstream of the cascade assembly, leaving a passage in this region, through which hole some of the deflected cold stream escapes, with a loss in efficiency as far as the directing of the said stream is concerned.
Last, and by no means least of the drawbacks, some of the deflected gases which do not escape via the cascades or this passage, are forced into the aforementioned cavity. This results in considerable noise which may be as high as 150 dB, and in risks to the structural integrity of the sliding cowl which has to be reinforced, leading to an increase in weight.
The object of the present invention is to overcome these drawbacks by proposing a reverser of the aforementioned type in which the radius Re of the exterior skin of the fan duct, taken in the plane P1 known as the xe2x80x9cupstream planexe2x80x9d, transversal to the longitudinal axis of the reverser and passing through the upstream end of the sliding cowl in a direct-thrust mode, is less than the maximum radius Ri of the interior skin of the fan duct, taken in a plane P2 known as the xe2x80x9cdownstream planexe2x80x9d, parallel to the plane P1 and downstream thereof.
By virtue of this arrangement, the spoiler part of the sliding cowl positions itself near the bulge of the interior skin of the fan duct after a shorter travel of the said cowl, hence there is the possibility of reverting to shorter actuators for maneuvering the sliding cowl.
Furthermore, when the spoiler part of the sliding cowl is near the bulge, the partition belonging to the upstream end of the sliding cowl may be in close proximity to the downstream edge of the cascade assembly, eliminating the possibility of the reversed gases emerging via the opening formed in the cowling without passing through the cascades, but above all preventing some of the gases from being forced into the cavity of the sliding cowl.